Damp at bottom of wall

[Kate8]

I’ve recently bought an old Victorian mid terrace that has had substantial ”renovations” done over its life. there was peeling paint above the skirting board - taking it off, it looks like a “text book” example of damp moving under a concrete floor and into the bottom of the wall. Would more experienced folks than me agree? Could people suggest options for either dealing with it or mitigating it? I’m guessing one option would be to have the floor replaced (would limcrete be the thing?) but I’m a recent first time buyer, with the accompanying low bank balance!

any help gratefully received.

 

[Cubist]

Hi Kate and Welcome,
Quite a few members have face similar problems in the past and I'm sure others will add their two-penneth soon. Some questions to get the ball rolling fr you: =

How sure are you that it's a concrete floor?
Is there any evidence of a Damp Proof Membrane beneath it?
Is there any evidence of damp in the floor-boards near the perimeter of the room?
Is the damage you are seeing associated with external walls only or are internal walls equally affected?

Excavating and replacing a concrete floor with limecrete would be a difficult, disruptive, time-consuming, messy and potentially expensive. May be an idea to ask others about alternative strategies they have used to mitigate or eliminate the problems other than totally replacing the floor.

Also, theres a better than good chance that the damp you are seeing in the walls is not rising from the ground below. It could be easily due to the transfer and evaporation of water from the concrete as it dried. Do you know or have any clue as to when the concrete floors were laid? I ask because the remedial work needed could be considerably easier and less expensive to implement.

Cheers for now,
Cubist

 

[Kate8]

Thank you!

The downstairs floor is covered with laminate - under the stairs it’s visible, and looks like concrete. The “stomp” test suggests the rest of the floor is solid. You can see plastic sticking up in the photo, between the edge of the laminate and the brick. It’s dry on one side and pretty damp on the other! This wall is a party wall - my neighbour doesn’t have anything against the wall on his side. There are signs of damp on the external walls - comapritively high moisture meter readings(I know not to rely on those too much!) faint tide mark and some loose paint, but I’ve been able to track potential sources of penetrating damp for most of them, so I’m hoping fixing those will help.

It was definetly laid before 2006, the earliest photos I have of the interior of the house. (At some point the staircase was moved and a cellar at the front blocked off. The cellar would be under the front room, this is at the back.)


I’ll take a better photo of the peeling paint when I can!

 

[Cubist]

Hi Kate,
The plastic is the exposed edge of a heavy gauge DPM that the concrete was poured and spread over. Given nearly 20 years the slab itself should be thoroughly dry and, unless there is or has been an active water leak, the slab is not likely to be the direct source of the damp problem. More likely, given it's a party wall, the source will be moisture rising through the brick-work from below immediate ground level. It's feasible the concrete floor and its DPM are contributing to this by pushing that rising moisture toward the walls.

You mention a cellar, do you have any access to determine if the affected walls continue down into the cellar itself?

Also, when you say its dry on one side and not the other what do you mean - is it damper between the plastic and wall than between the plastic and the laminate or, do you mean in your neighbours house?

Cheers for now,
Cubist

 

[Kate8]

Thank you! The cellar has been completely blocked off unfortunately - it would have been under the front room, and this is the back.

It’s damp between the plastic and the wall, and dry between the plastic and the laminate. The neighbour doesn’t have any issues on his side

 

[Cubist]

That's pretty much what I was expecting. The issue is damp rising through the brickwork and wicking to the atmosphere through the softer plaster and woodwork. Provided that both you and your neighbour have no past or current water leaks its certainly groundwater rising from the foundations/footings of the house. It's likely that the paint that has been peeling off the wall is non-breathable, or considerably less permeable than it needs to be, and moisture is getting trapped between it and the plaster causing the paint to crack and flake.

It may be fair to assume also that unless the walls have been re-plastered since the house was built then lime plaster would have been used. You can test for lime mortar or plaster by spraying a little vinegar over a small area and watching for a fizzing action. No fizz its likely gypsum plaster. It's also worth checking the rear face (the wall side) of the skirting boards you have removed - is there or was there any evidence of blackening of the wood or presence of black/dark molds? This can sometimes be used to gauge just how damp they became but your photos indicate little evidence of this on what's shown.

The good news I think is that you probably don't need to dig up the floor and replace everything. Thoroughly stripping the paint off the walls, making good any plaster damage and re-painting with a breathable paint would be as much as I would do. Beyond that you should also ensure good ventilation is maintained in that room if at all feasible.

Hope this helps for now and also that some of the other members here chip in with any other suggestions.

 

[stuart45]

If it's had substantial renovations, it's quite likely that the lime plaster was replaced with gypsum. If this is the case, then consider replacing it with lime.

 

[Lacan07]

Hi Kate,
The plastic is the exposed edge of a heavy gauge DPM that the concrete was poured and spread over. Given nearly 20 years the slab itself should be thoroughly dry and, unless there is or has been an active water leak, the slab is not likely to be the direct source of the damp problem. More likely, given it's a party wall, the source will be moisture rising through the brick-work from below immediate ground level. It's feasible the concrete floor and its DPM are contributing to this by pushing that rising moisture toward the walls.

You mention a cellar, do you have any access to determine if the affected walls continue down into the cellar itself?

Also, when you say its dry on one side and not the other what do you mean - is it damper between the plastic and wall than between the plastic and the laminate or, do you mean in your neighbours house?

Cheers for now,
Cubist

Its interesting isn't it that even when a concrete floor is laid down with a proper DPM it still causes trouble. As you say moisture coming up from beneath the floor which is unable to escape may be pushed laterally (under pressure) to all sides. And there's no easy way to retrogressively tie that membrane into the surrounding double brick wall. Concrete floors are fine when installed properly in a new build when you can detail the DPC between the floor and wall.

 

[stuart45]

Used to happen on some new builds in the 70's, when it was common practice to cut the DPM flush between the slab and inner skin to make it easier to lay the first course of block work. At the time BRE recommended 3 coats of Sythaprufe at the wall/floor junction to help stop the damp.

 

[Willsa]

Concrete floors and plastic sheets in old houses just fill me with dread now!
My damp proofing membrane also had the "dew" on one side...

OK, so shut-off cellar void at the front, what room is the one with damp and what's underneath that room? Is it a suspended concrete floor or a solid slab?

I suspect it's suspended (unless it's in a kitchen extension ). And I bet that there is too much water and too little air in that void for your house to function properly.

What water ingress problems are you recognising on the outside?

Just don't put that skirting back on until you're sure that the remedial works are done and the dew has stopped forming - it's the perfect conditions for dry rot fungus otherwise.

 

[Willsa]

Also, it seems from the second photo that the brick walls are rendered in hard cement, then skimmed in pink-ish gypsum, then painted?

 

[Lacan07]

Also, it seems from the second photo that the brick walls are rendered in hard cement, then skimmed in pink-ish gypsum, then painted?

Yes, thats definitely a gypsum skim, not sure about the cement but you could be right about that too.